The environment of structured floor substrates (reefs, rock and debris fields) in bodies of water as well as of artificially created underwater structures (platforms, wreckage, artificial reefs) is an agglomeration point for a wide variety of usable crab types. Especially in offshore areas, these regions are often rarely farmed. Conventional trawling nets can only be used at a high risk given the danger of entanglement. By contrast, baited traps are less lucrative for use on the high seas because of their large size and the high cost per animal caught. Large crabs have previously been trapped on structured hard substrates or artificial structures using bow-net systems or baited trap systems. Generally constructed for coastal use, these systems are in part also used in offshore areas. Artificial reefs for colonizing certain hard-bottom fauna are being developed with various approaches.
U.S. Pat. No. 4,736,708 describes a transportable device for colonizing and harvesting crab types consisting of a series of individual barrel-shaped elements, which are connected between two floor anchors by a line. Such a device is relatively bulky, and hence difficult to bring out and haul back in.
U.S. Pat. No. 4,982,525 describes a collapsible lobster trap consisting of a triangular floor grid and three triangular lateral grids. The lateral grids are connected with the floor grid by hinges. The unused lobster trap is transported while in a collapsed state, and harvesting takes place when it is deployed in the shape of a tetrahedron, wherein the lateral grids contain through openings for the lobsters. The lobster traps are also lowered and raised in a deployed state. The lobster trap is only intended to be lowered for a short time, and is not suitable as a habitat, since the crabs are trapped immediately.
U.S. Pat. No. Des. 401,994 shows a collapsible lobster trap in which a vaulted grid array of lateral grid flaps can be closed. The vaulted grid array consists of a grid plate that is hinged on one side to a floor grid. When stored, all grids sit flatly on the floor grid. Before lowered, the grid plate is bent into a vaulted structure, and locked in place on the floor plate with a hook. The grid flaps can be adjusted in terms of their working angle relative to the vaulted grid array. In the lowering process, the ropes pull the grid flaps toward the vaulted grid array, after which the grid flaps sit on the floor of the body of water once the ropes have been released and slackened, opening up the interior of the vaulted grid array. When hauling in the lobster trap, the vaulted grid array is then closed by the grid flaps by tensioning the ropes. This lobster trap is also suitable as a habitat, but is not all that attractive to crabs.
FR 2 345 914 A1 describes a net with an oval cross section for catching oysters. The net has an oblong opening cross section with lateral curvatures. The net is closed by means of a device consisting of two plates interconnected by a central hinge, each shaped like half the opening cross section. This device is introduced into the net in a collapsed state and then opened, so that the plates are arranged at an opening angle relative to each other. Pressing down the central hinge aligns the plates in a plane, giving them a width that now exceeds the width of the opening cross section, causing the device to become lodged in the net. The hinge is overstretched in order to lock the hinge in place, thereby preventing the plates from folding back. However, the net is not suitable for catching benthic organisms.
DE 101 61 174 C1 describes a transportable aquaculture breeding unit for colonizing and harvesting sponges. To this end, the aquaculture breeding unit consists of two quadrilateral frames, which incorporate grids as seeding and trapping surfaces. The two frames are hinged together at their opposing inner transverse sides by means of a central hinge. The central hinge exhibits a one-way folding direction. Two different positions are provided for both frames. When deployed, the two frames lie one atop the other (opening angle of device 0°), forming a closed box, as it were, and the sponges can propagate from the colonizing and trapping surfaces into its interior. The device is also hoisted in the collapsed state. For harvesting purposes, the two frames are opened and, if necessary, folded open until forming a plane (max. opening angle of device 180°), so that the colonized sponges can be readily removed. Several of these devices can be combined to form large structures, for example in a zigzag pattern.
This device is geared toward the seeding and harvesting of immobile sponges, and benthic, invertebrate, mobile (vagile) animals are difficult if not impossible to breed, since the habitat is here not attractive enough. Trapping is also not possible, since the vagile animals are able to exit the collapsed device as it is being lifted. In addition, the known device by itself does not permit any adaptation to the arising floors in the bodies of water, but can only lie flat on the floor of the body of water. Only when several devices are combined can an adjustment be effected. However, this complicates the lowering or retrieving process, or necessitates a relatively complicated underwater assembly.